timber house extension

[Telfmann]

I am hoping to one day build a small bedroom at the rear of our house. And was wondering if anyone else has built or is considering a extension made out of timber. My house is of conventional construction, bricks walls, tiles on the roof ect, and i would like to build a one storey extension aprrox 8 x 12', just enough to fit a single bed at the far end. I have read about walter segal buildings and this seems like a cost effective method, using 4x4 posts, and stud walls sheathed in 3/4" plywood. If anyone has any ideas about how to add a extra room to there house then please respond to this post. Information on structual insulated panels (i.e. can i just buy them off the shelf), flat roofing (using a rubber membrane), or foundations (would concrete pads be better than a sill plate) would be most appreciated.

[The Natural Philosopher]

I have seen this done round here extesnively - and teh usual method is to build brick /block up to about a foot above damp coure, and do the stud/timber frame above that.

The exterir ply can be carried over down to damp lebvel; and drip beaded there.

Internally unless you use massive wall thickness, there will be a ledge below teh sill plate, but hey, its all 'feature'

You could take the timber down to damp level, but I would be nervous of that.

In my house we used 7" thick walls and filled em with rockwool. 4" for internal walls only.

Breathable membrane over the ply, battens running vertically and metal lath rendered over, on top. Airgap between render/lath and ply.

To tie into existing brickwork is just a question of strapping or even screwing to it., Damp proof between studs and existing brick probably a good idea.

Don't like flat rooves meself. Make sure the flashing where it butts existing wall is done properly - lead keyed into courses, and laid over roofing membrane which should run up wall behind lead etc.

I am not an architect. Suggest you consult one.

[John Rumm]

No reason why you can't build out of studwork. You can meet the required insulation values stipulated in the building regs with thinner walls as well.

You would need foundations just as you would for a blockwork extension. The main structure would typically be built with 4x2" on 400mm centres. Probably 6x2" for roof timbers (assuming a flat roof). Insulation would be with urethane or polyisocyanurate (PIR) foam which is readilly available from a variety of sources (common brands include Celotex, Kingspan, Ecotherm, Rubberoid etc).

The outside walls could be 1/2" or 3/4" ply. You could render over the top of that.

[IMM]

Get the book "Out of the Woods" about the Segal method. Very good, and gives the technique in detail. The problem is that you will need a structural engineer to do the timber frame calcs for you. Some may do it on the side as it is only a small extension. Insulate the floor and walls very well. Seal up with silicon.

SIP panels:

Look at this book: Building with Strucutural Insulated Panels (SIPs): Strength and Energy Efficiency Through Structural Panel Construction By Michael Morley ISBN: 1561583510

Synopsis Structural insulated panels are sandwiches of foam insulation between two sheets of fibreboard or plywood, and are used to build walls, roofs and floors in all kinds of modern buildings: instead of three components - a frame, insulation and sheathing - SIP panels are all three things and come ready to install. SIP- constructed buildings are vastly more efficient, quicker to build, stronger, quieter and more draught-free than older post-war building systems. Taps into a huge and growing self-build market which is generally only served by technical books.; Tips and information on this highly efficient building material from an expert builder who specialises in structural insulated panel construction. Packed with 180 colour photographs and 40 drawings.; Takes the reader through the entire process of building a panel-constructed house, from planning and estimating, ordering, storage and handling to construction.

Some SIP companies:

at "I" beams: you have absorbed much of this come back with more questions. This will do for now.

[IMM]

No you would not. The Segal method is post and beam with minimal foundations. The foundations consist of a 1 metre squ. hole by 1 metre deep filled with concrete with a paving slab on top. The post rests on this. Six of these is good enough for his extension.

See the book Out of The Woods which gives all the choices for Segal.

[John Rumm]

Erm, what exactly are you dissagreeing with? So these these segal blocks are not foundations then? Weather you have blocks as you describe, or strip/beam fill, you still need foundations!

Something similar in design to those used on the rest of the property might be a good idea as well, if the new structure is to be fixed to the existing (the importance will depend on the local soil composition).

[IMM]

A block work extension needs strip foundations. Find out how Segal do it.

You don't say... Six small holes in the ground is very different to strip foundations, although strip foundations are a part of the Segal method, in its rawest and most basic form Segal has minimal foundations, that any DIYer can do, and the rest is none wet trades work making it easy for a good DIYer with common sense and power tools to tackle. Complete novices have built Segal homes, that is it's attraction. Some very attractive wooden framed Segal homes have been built. they are not all low cost homes for low income people.

Where there is poor soil composition Segal scores. The odd deep hole here and there to support a post. is all you need. You can hire a drilling machine to drill quite deep onto a hard surface beneath the soil. Segal homes are mainly off the ground with any form of cladding you want to blend in with anything.

The only negative aspect of the basic Segal method is elimination of cold bridging. Although this can be done at extra expense.

[The Natural Philosopher]

However the cost is similar. Been through the calcs as to whether to use piled or strip foundations. Bugger all difference, but the trades to do strip are easier to find, and teh BCO doesn't purse his lips so much.

Whatever the final answer, having timber work that can be splashed by rain is a Bad Idea.

It doesn't actually. To the simple minded it looks cheaper, because its just less concrete, but the actual process of making the holes is far more complex than a JCB digging a trench.

[IMM]

If the soil is poor, piled is the only sensible answer.

See the Segal site. Any problems with BCOs and they will intervene.

You have large roof overhangs to reduce/eliminate rain on the building sides, or have jettied upper floors too. Theses were designed specifically to keep rain from the sides of wooden buildings many 100s of years ago. They look neat too. Having rain off the walls prevents the house from cooling. It also keeps the sun off in summer too.

If the soil is fine, digging by hand, six 1m x 1m holes is not a big thing at all.

[John Rumm]

You miss my point I believe... All I was saying to the OP is that you will need foundations of some sort. Just in case he was thinking along the lines that using studwork to build the extension was going to free him from that requirement. I was not suggesting that Segal or any other method was good or bad - each have pros and cons.

[Telfmann]

Thanks to everyone who has viewed this post, and especially to the ppl who have responded.

Out of the woods is a great little book, and packed full of information and useful ideas, but after weeks looking at the same 2D picture of a wall made with 4x4 posts and searching on the internet, i decided to buy some american books, which showed practical ways of doing things.

'Timber framing for the rest of us' details exactly how to connect a sill plate to a foundation. 'Practical pole building construction' shows how horizontal timber (girders) would attach to posts and allow sheathing to be fastened.

Its true that most segal buildings you hear about are built on foundation pads, but in 'out of the woods' it also describes ataching a sill plate to a slab foundation (as mentioned in a post above). I do think however that the timber would be better off the ground by a few inches, as this would reduce the rain and mud splashing onto it. Although self build does not mean 'on the cheap', i hope there is a still a place for low income housing for low income families. As not everyone can afford or would want to live in a goldfish bowl in the middle of a forrest.

And to increase my chance of getting planning permission, and building a sound structure, a architect would likley be needed. Of course the idea of just building a shed (a shed you could call home) and using that as a play room has also occured to me.

[Telfmann]

Its alot to take it, im working my way through your websites. I agree insulating the floor is very important, expecially if it off the ground with wind whistling underneath. Role on the day when you can buy SIP's from Wickes.

[IMM]

I have seen a few Segal houses and theyn look good. They look eco.

For a single floor extension? They just want simple drawings and stress calcs.

God ones cost 12K, best build Segal.

[IMM]

In the US you can. They have catalogues of various sizes of panels with doors windows already cut in. Just pick and fix and a weatherproof shell up in days. AS most of their houses are bungalows and you don't need scaffold around the house (exspensive) a couple of men can put the SIPs up in a few days, even the roof. SIPs is the way forward without doubt. Total elimination of thermal bridging.

[IMM]

Do these books go into TJI "I" beams?

[The Natural Philosopher]

No, just bookcases, John, just bookcases...

[IMM]

A mentalist enters.....

Sad isn't it.

[Telfmann]

they also go into I-beams, as there is a handy shelf provided in the middle of them, along the lines of the handy pop out beverage holder that comes with a pc.

Unfortuanalty they don't discuss I-beams within the book, 'practcal pole construction' is from the 80's, but does have great info on loading poles, how to increaase loading on a post from 3 tons to 16 tons, by using spiked connectors instead on nail (nails, lol) or bolts (6 tons). Although the book deals with telephone poles ect stuck into the ground, alot of the other info is relevant for hanging walls off posts. 'Timber framing for the rest of us' is a 2004 book but is mainly about connecting large dimensional lumber (8"x8") with joist hangers and toe-screwing, to sill plates and posts on a dpc. Such large timbers are used because the aurthor likes turf roofs, but he also mentions 'out of the woods'. I-beams would be a great alternative to using large timber in this situation, but does not mention it in this book, however there are very detailed step by step guides and span charts.

[IMM]

There must a book out there that covers TJI "I" beams and normal cut timber. TJI's are now even common in the UK. Five years ago people scorned these as ticky tacky. Now they are mainstream. The Brits are slow learners.

Maybe the TJI makers can recommend a book.

[Telfmann]

Its true that the british never seem to take up a good idea quickly, the bluestreak rocket, tilting trains, the digital computer (or mechanical for that matter), but alot of american households don't have a electic kettle, how do they manage.